Cell Cycle Flashcards
What is the principal role of the cell cycle?
To produce two genetically identical daughter cells?
Why are the gap phases necessary?
Need to grow in-between divisions otherwise cells would get smaller over time
What are the two main phases of the cell cycle?
Interphase and mitosis
What are the 3 subphases of interphase?
G1 - Gap phase
S - Synthesis phase
G2 - Gap phase 2
What is G0?
A non-dividing, differentiated state
Which phase are most human cells in?
G0
Example of cells in G0
Liver cells, but can be ‘called back’ into the cell cycle
Which cells are ‘arrested’ in G0?
Nerve and muscle cells
What occurs during the gap phases?
Cell checks and growth
What occurs during the synthesis phase?
DNA replication
What occurs during M phase?
Nuclear and cytoplasmic division
Stages of mitosis
Prophase Prometaphase Metaphase Anaphase Telophase (cytokinesis)
What occurs during prophase?
- Sister chromatids condense
- Mitotic spindle assembles between two centrosomes that have moved apart
What occurs during pro metaphase?
- Nuclear envelope breaks down
- Chromosomes attached to spindle microtubule via their kinetochores
- Movement of chromosomes begin
What occurs during metaphase?
- Chromosomes assemble along the equator
- Kinetochore microtubules attach sister chromatids to opposite poles of the spindle
What occurs during anaphase?
- Sister chromatids separate to form two daughter chromosomes –> each pulled towards spindle pole
- Kinetochore microtubules shorten by depolymerisation at their kinetochore ends and spindle poles move apart
What occurs during telophase?
- Two sets of daughter chromosomes arrive at the spindle poles and decondense
- Nuclear envelopes form around each set to produce two nuclei
What is cytokinesis?
Cytoplasm is divided by a contractile ring of actin and myosin filaments to form two cells from one
What are the three classes of microtubules involved in mitosis?
- Astral: help to position the spindle correctly
- Interpolar: help to stabilise the interpolate spindle
- Kinetochore: help separate the sister chromatids
When is the main checkpoint in the cell cycle?
Metaphase
-If chromosomes don’t pair up –> negative signal released
- all attached –> positive signal
nature of signals: phosphorylation and preoteolysis
What is the nature of the signals that are released at checkpoints?
Phosphorylation and proteolysis
In Xenopus, what is the cell cycle regulated by?
Cyclin-dependent kinases (Cdk)
What does Cdk require for activity?
Cyclin
What is Cdk further regulated by?
Phosphorylation/Dephosphorylation
Is the level of cyclin constant throughout the cell cycle?
No, they are synthesised and degraded throughout
Is the level of Cdk constant through the cell cycle?
Yes, relatively
What are cyclin levels regulated by?
The anaphase-promoting complex
What controls the metaphase-anaphase transition?
Proteolysis
